This invention is generally directed to processes for generating colored images of consistent quality for a substantial number of imaging cycles, and wherein the toners selected retain their triboelectric characteristics, and possess excellent admix characteristics. More specifically, there are provided in accordance with the present invention processes for generating images and prints of high quality with a color developer composition that retains its triboelectric charging properties for in excess of 500,000 imaging cycles. Further, in accordance with the present invention, the triboelectric charging values desired for the color toners can be preselected, that is the level of charge and the direction of this charge can be predetermined. The aforementioned toner and developer compositions also possess excellent fusing characteristics. Specifically, thus the toner compositions of the present invention comprised of specific mixture of polymers are useful in xerographic imaging and printing processes, inclusive of those embodied by the commercially available Xerox Corporation 9700.RTM. and 5600.RTM. apparatuses. In these apparatuses, the developer compositions of the present invention possess stable triboelectric charging characteristics for the entire imaging sequence; and further, these triboelectric charges can be preselected, properties not readily achievable with many prior art processes and compositions. Moreover, with the process and developer compositions of the present invention, there are permitted other outstanding characteristics as disclosed hereinafter inclusive of rapid admix properties.
Toner compositions, inclusive of colored toner compositions, are known. These compositions are generally comprised of resin particles, pigment particles selected from cyan, magenta, yellow, red, green, blue, or mixtures thereof; and optional additive particles including, for example, metal salts of fatty acids, and colloidal silicas. The triboelectric characteristics of the aforementioned colored toners are generally determined by the particular pigments selected. Additionally, the level and direction of charge can be significantly altered depending on the selection of the polymer component within which the pigment is dispersed. Accordingly, with only a limited number of acceptable toner resins, and the scarcity of desirable charge enhancing additives, the ability to modify the triboelectric properties of colored toners is rather limited. One problem solved with the process of the present invention enables the selection of a wide variety of polymers while simultaneously enabling colored toner particles with preselected stable triboelectric charging characteristics; and wherein the aforementioned toner compositions possess good admix characteristics, that is new uncharged toner particles added to the imaging apparatus, acquire the appropriate polarity and triboelectric charging value in a rapid time period less than, for example, 5 minutes. This is accomplished primarily by the mixing of polymers as illustrated hereinafter.
There is disclosed in U.S. Pat. No. 3,669,922 colored thermoplastic powders which can be prepared by grinding coarse colored film of plastic cubes or pellets to the desired sizes. These powders can be obtained by incorporating pigments or dyes in a mixture or blends of resins which are subsequently passed through a high shear pulverizing device, reference column 1, beginning at line 57, and continuing on to line 67. This patent, however, is silent with respect to, for example, achieving rapid admix with constant triboelectric charging characteristics for toner compositions. Further, it is known, for example, that additives such as Aerosil will have a tendency to increase the negative triboelectric charging values on the toner compositions while simultaneously adversely affecting the admix charging time periods. The aforementioned problem is substantially eliminated with the process of the present invention.
Further, there is disclosed in U.S. Pat. No. 4,457,998 improved developer compositions comprised of toner particles containing an uncrosslinked polymer incorporated into a polymer network which has been highly crosslinked in the presence of the uncrosslinked polymer, and uncrosslinked polymer being of a different composition than the crosslinked polymer. As examples of uncrosslinked polymers, there is illustrated in this patent styrene/alkyl acrylate polymers, and styrene butadiene polymers; and a crosslinked polystyrene/n-butylmethacrylatemaleic anhydride terpolymer.
In U.S. Pat. No. 4,473,628 there is illustrated a toner with emulsions of two polymers having different characteristics. More specifically, in accordance with the teachings of this patent, there is described a toner for developing electrostatic latent images with a binder resin prepared by mixing two emulsions, coagulating the emulsion mixture, separating the solid from the latent, and dehydrating into a solid product. One preferred example of the mixed resin that can be selected is a mixture of styrene butadiene copolymers, reference column 2, beginning at line 15. In accordance with the teachings of this patent, the toner was designed in a manner so as to possess acceptable rheology with no teaching therein as to obtaining simultaneously stable triboelectric charging values and rapid admix charging characteristics.
Additionally, there is disclosed in copending application U.S. Ser. No. 655,381, entitled Toner Compositions With Crosslinked Resins and Low Molecular Weight Waxes, an improved positively charged toner composition comprised of a polyblend mixture of a crosslinked copolymer composition and a second polymer, pigment particles, a wax component of molecular weight of from about 500 to about 20,000, and a charge enhancing additive. The disclosure of the aforementioned copending application is totally incorporated herein by reference.
Moreover, disclosed in copending application Ser. No. 681,177, entitled Process for Achieving Consistent High Quality Images With Magnetic Developers, is a process for generating consistent high quality images for extended periods, and wherein the developer retains its electrical properties for over 2.5 million imaging cycles. There is selected for the aforementioned process a stable two-component developer comprised of resin particles, first pigment particles, second magnetic pigment particles, and blended flow additive particles. The disclosure of the aforementioned copending application is totally incorporated herein by reference.
Therefore, there is a need for colored toner compositions wherein the triboelectric charging characteristics thereof can be preselected. Also, there is a need for stable colored developer compositions that will enable the generation of developed images with exceptional quality, and further, wherein these compositions will maintain their triboelectric charging properties for substantially unlimited imaging cycles. Additionally, there is a need for imaging processes with colored developer compositions that possess reduced aging characteristics in xerographic imaging and printing systems. Aging, a prevalent problem in many xerographic imaging processes, involves for example continuous reduction in toner charging capability, which eventually causes copy quality degradation as is evidenced, for example, by excessive background printout. Accordingly, the present invention enables xerographic imaging and printing processes with colored developer compositions that retain their triboelectric properties, and in particular their triboelectric charging values for an extended number of imaging cycles, exceeding 500,000 for example. In contrast, with similar prior art imaging processes using colored developer compositions, a triboelectric charge typically, undesirably decays continuously beginning with about 100 imaging cycles. Furthermore, there remains a need for colored toner compositions with selected triboelectric characteristics which simultaneously possess acceptable fusing properties. Also, there is an important need for toner compositions which simultaneously possess excellent admix characteristics thereby enabling uncharged toner particles added to the imaging apparatus to achieve the appropriate constant triboelectric charging value within a short time period, for example prior to 5 minutes.